CSL has developed a computer system, now in operation in the Radiation Oncology Branch, NCI, to use the detailed contour and density information available from computer assisted tomography to improve radiation treatment planning. The system allows the radiotherapist to review scans of the tumor area at a color video terminal, quickly varying the presentation of the image to emphasize a particular structure or magnify an interesting feature. Outlines of tumor or vital organs, in some cases drawn automatically by the computer are then processed by software purchased from Atomic Energy of Canada, Ltd. to provide sophisticated individualized treatment plans.